DESCRIPTION: Successful treatment of pancreatic adenocarcinoma (PDAC) remains a challenge due to the desmoplastic microenvironment that promotes both tumor growth and metastasis and forms a barrier to chemotherapy. Hedgehog (Hh) signaling plays a crucial role in PDAC progression and contributes to desmoplasia. Hh inhibitor GDC-0449 can overcome desmoplastic reaction. While Hh levels are increased in pancreatic cancer stem cells (CSCs), tumor suppressor miR-let7b targets several genes involved in PDAC pathogenesis. Therefore, inhibition of Hh pathway and restoration of miR-let7b could effectively treat PDAC. In our preliminary studies, miR-let7b was downregulated in pancreatic cancer cell lines, human patient's cancer tissues and during progression of spontaneous pancreatic cancer in genetically engineered KPC mice. Our in-silico analysis and in vitro experiments indicate that miR-let7b targets several genes like MUC4, NCOA3, Kras, HMGA2 and TGFR1, which are upregulated in PDAC. miR-let7b and GDC-0449 could inhibit the proliferation of human pancreatic cancer cells (Capan-1, HPAFII and T3M4) and there was synergistic effect when miR-let7b and GDC- 0449 were co-formulated into micelles using poly(ethylene glycol)-block-poly(2-methyl-2-carboxyl- propylene carbonate-graft-dodecanol-graft-tetraethylenepentamine) (PEG-b-PCC-g-DC-g-TEPA) copolymer. This copolymer self-assembles into micelles and encapsulates hydrophobic GDC-0449 into its core and allows complex formation between miR-let7b and cationic pendant chains. This combination therapy effectively inhibited tumor growth when injected to ectopic tumor bearing mice compared to micelles carrying GDC-0449 or miR-let7b alone. Cetuximab, a monoclonal antibody for EGFR receptors, was conjugated to the nanomedicine to achieve active targeting to PDAC. Therefore, we hypothesize that combination therapy of miR-let7b with GDC-0449 using cetuximab conjugated nanomedicines can effectively chemosensitize PDAC cells by reducing desmoplasia and treat PDAC by reducing their tumorigenicity. Our overall objective is to develop novel combination therapy for PDAC using nanoformulations targeting multiple signaling pathways by miR-let7b and Hh pathway by GDC-0449. Our specific aims are to: i) determine the efficacy and molecular mechanisms of miR-let7b and GDC-0449 combination therapy in PC cells; ii) co-formulate miR-let7b and GDC- 0449 in cetuximab conjugated polymeric micelles and assess their synergistic effect on the inhibition of pancreatic cancer cells, iii) determine the therapeutic efficacy of micelles encapsulating miR-let7b and GDC-0449 in orthotopic NSG and genetically engineered KPC mouse models of PDAC. Long- term significance is to develop nanomedicines of miR-let7b and GDC-0449 that increase the local drug concentrations within the fibrotic stroma of these tumors and bypass the resistance mechanisms that allow tumor growth and inhibit the efficacy of current standard chemotherapies.